How to Build a Greenhouse

1.1. The best location to build a greenhouse is on the south side of your property where it’ll be exposed to the most amount of sunshine. If that’s not possible, then locate it on the east or west side of your yard, so it’ll get morning or late-afternoon sun. Wherever you choose to place your greenhouse, make sure the area is not too shady. Here are a few other considerations:

• Sun exposure: The location should receive plenty of direct sunlight, as plants need light to grow.
• Easy access: The location should be easily accessible for watering and maintenance.
• Drainage: The location should have good drainage to prevent water from pooling around the greenhouse.
• Wind: The location should be protected from strong winds, which can damage the greenhouse or plants.
• Temperature: Consider the average temperature and climate conditions in the area.

2.1. Clear the area where you want to build the greenhouse and layout for the foundation, using the below illustration as a guide.

2.2. For the foundation, use a power auger to dig ten 8″ diameter holes to a depth of 2′.

3.1. Mix up a batch of concrete and pour it into the holes, filling each one flush with the surrounding ground. Let the concrete cure overnight. 

3.2. Once concrete has cured, foundation is ready for the next step.

7.1. Build the left wall entirely out of pressure-treated 2x4s, including five wall studs cut to 6′-9″, and the top and bottom wall plates each cut to 7′-5″.

7.2. Attach the parts with 5″ screws.

7.3. Using a carpenter’s framing square, check the corner to make sure they are 90°.

9.1. Cut the seven roof rafters out of pressure-treated 2x6s, as shown in the drawing below. Cut each rafter to 9′-2 1/4″. Trim one end of each rafter to sit flush with the top plate on the rear wall. Then, cut a bird’s mouth notch at the opposite end of the rafters, so they sit flat on the top plate of the front wall.

9.2. Fasten the rafters with 5″ screws.

10.1. Cut pressure-treated 2x4s to form the studs in the upper section of the left and right gable-end walls. Using drawing below as a reference, cut two 2×4 studs to 1′-11 1/2″ and two 1′-1/4″. Then cut two 2x4s to 3′-7 1/2″ to frame the rough opening for an air vent.

10.2. Fasten the gable wall studs with 5″ screws.

10.3. Using a carpenter’s framing square, check the corner to make sure they are 90°.

11.1. Cut 5/16″ polycarbonate panels into five pieces for the front wall, using the drawing below as a reference. Cut two pieces to 3′-6″ x 7′-4″, two to 3′-6″ x 4′-4 3/4″, and one to 8 3/4″ x 5′ sheet.

11.2. Secure the polycarbonate with 1″ screws and washers.

12.1. Cut 5/16″ polycarbonate for the back wall, using the drawing below as a reference. Cut three pieces to 4′ x 7′-6 3/4″.

12.2. Secure the polycarbonate with 1″ screws and washers.

13.1. Cut 5/16″ polycarbonate for the left wall, using drawing below as a reference. Cut two pieces to 4′ x 7′-2″, one to 2′-7 1/4″ x 4′, and one to 2′-5 3/4″ x 4′ sheet.

13.2. Secure the polycarbonate with 1″ screws and washers.

14.1. Cut 5/16″ polycarbonate for the left wall, using drawing below as a reference. Note that these four parts are identical to the parts cut for the left wall.

14.2. Cut two pieces to 4′ x 7′-2″, one to 2′-7 1/4″ x 4′, and one to 2′-5 3/4″ x 4′ sheet.

14.3. Secure the polycarbonate with 1″ screws and washers.

16.1. Build the two hinged greenhouse doors out of pressure-treated 2x4s; join the parts with 5″ screws. Cut six 2x4s to 2′-2 1/4″ for the horizontal rails, four 2x4s to 7′-1 3/4″ for the vertical stiles, and four 2x4s to 3′-11 1/2″ to serve as diagonal braces. 

16.2. Cut two 5/16″ polycarbonate sheets to 2′-5 3/4″x 7′-1 3/4″ to cover the doors.

16.3. Secure the polycarbonate with 1″ screws and washers.

16.4. Attach each door to the front wall with two hinges. Also install a handle to each door.

17.1. Next, make the four air vents for the greenhouse. There are two vents above the doorway and one on each end wall of the greenhouse. The vents are necessary to prevent the interior of the greenhouse from getting too hot. 

17.2. As shown in Node A (page 28), build the rectangular frame for the vents that go above the doorway out of pressure-treated 2x4s. Cut four 2x4s to 2′-4 3/4″ for the horizontal top and bottom of the frame, and four boards cut to 3′-1/4″ that will be vertical slides of the frame. Fasten the frame together with 3 in. screws.

17.3. Cut two pieces of 5/16″ polycarbonate to 2′-4 3/4″ x 3′-3 3/4″ and secure them to the vent frames with 1 in. screws and washers. 

17.4. According to the Node B (page 28), build the ventilation frame for each side wall using pressure-treated 2x4s. Cut four 2x4s to 3′-3 1/4″ and four to 1′-11 1/4″. Fasten the frame together with 3 in. screws.

17.5. Cut two pieces of 5/16″ polycarbonate to 1′-11 1/4″ x 3′-6 3/4″, then secure them to the vent frames with 1″ screws and washers.
17.6. Fasten the vents to the greenhouse with hinges and 1’ screws. Then, according to the Node C (page 29), install a hook-and-eye closure to each vent.

18.1. Build two potting benches for the interior of the greenhouse. The benches provide a convenient work surface for potting and pruning plants, and below the work surface is a handy storage shelf. Here are detailed step-by-step instructions for building the benches:

19.1. Build the structural frames of the two potting benches out of pressure-treated 2x4s. Cut the eight 2×4 legs to 4′, and then cut eight 2x4s to 2′ for the horizontal end rails, and eight 2x4s to 5′ for the horizontal rails along the front and rear of the frame. 

19.2. Fasten the frame parts together with 3″ screws.
19.3. Using a carpenter’s framing square, check the corner to make sure they are 90°.

20.1. Cut short lengths of pressure-treated 2x4s to span between the front and rear rails, as shown below. Cut twelve 2x4s to 1′-9” and secure them with 3″ screws.

20.2. Using a carpenter’s framing square, check the corner to make sure they are 90°.

21.1. Cover the work surface and storage shelf with 5/8″ plywood. Cut four plywood pieces to 2′ x 5′-3″.

21.2. Fasten plywood to the 2×4 frame with 2″ screws.

21.3. Apply two coats of exterior-grade marine varnish to plywood.